Radial

Neither acoelomate, psuedocoelomate or coelomate.

• Central digestive compartment is the gastrovascular cavity.
• After the animal ingests the food, the gastrodermis secrets digestive enzymes into the gastrovaascular cavity. The gastrodermal cells engulf small pieces of the partially digested food by phagocytosis and digestion is finished within the cells in food vacuoles.

Water is pumped in and out of the gastrovascular cavity; flagella on the gastrodermal cells help distribute nutrients.

Oxygen diffuses across the surface.

Undigested remains are egested through the mouth/anus.

• Muscles move by cell layers contracting by contractile fibers
• movements are coordinated by a nerve net associated with simple sensory receptors distributed radially around the body.

In most polyps (a type of cnidaria with tentacles), reproduction consists of asexual “budding”. Sexual formation of gametes is prevalent in medusas (cnidaria that moves by contractions of its bell-shaped body) and some polyps.

• Some cnidarians are dimorphic, and can be a polyp at one stage in their life and medusa in another.
• tentacles are armed with batteries of cnidocytes, cells that function in defense and aid in the capture of prey.